One of properties demanded for oil well pipes is collapse strength for preventing the oil well pipes from being broken even deep in the ground. The collapse strength is measured in terms of collapse pressure.
It has been known that in an electric resistance welded steel pipe used as an oil well pipe (hereinafter also referred to as “electric resistance welded steel pipe for oil well”), a collapse strength is increased with decreasing the ratio (D/t) of an outer diameter (D) to a wall thickness (t), increased with increasing a yield strength (YS), increased with decreasing a residual stress (a residual stress generated in the pipe in a step carried out in a cold forming condition, such as forming or sizing of the electric resistance welded steel pipe), and increased with increasing excellence in roundness and thickness deviation, (see, for example, Non Patent Document 1).
As techniques for the purpose of enhancing the collapse strength of an electric resistance welded steel pipe for an oil well, a technique of making the pipe, and then performing heat treatment at low temperature to increase the yield strength utilizing the Cottrell effect, thereby enhancing the collapse strength (see, for example, Patent Document 1), and a technique of making a pipe, and then performing heat treatment at high temperature to remove residual stress, thereby enhancing the collapse strength (see, for example, Patent Document 2) are disclosed.
A technique of adjusting the chemical composition, yield stress (yield strength), tensile strength, and yield ratio of an electric resistance welded steel pipe for an oil well into specific ranges, respectively, whereby the strength and toughness of the pipe are improved without performing heat treatment after pipe making, has been known (see, for example, Patent Document 3).    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. S60-187664    Patent Document 2: JP-A No. S59-177322    Patent Document 3: Japanese Patent No. 5131411    Non Patent Document 1: Journal of the Japan Society for Technology of Plasticity (journal of JSTP), Vol. 30, No. 338 (1989-3)